This revised proposal is from a well established investigator who has made seminal contributions to the field of insulin action and now to the field of beta cell physiology. This proposal is based on recent data generated by the principal investigator using gene ablation in mice of IRS1 and IRS2, in combination with mice lacking one allele of the IGF-1 receptor. These data, recently published in Nature Genetics, strongly suggest that IRS2 is a key determinant of pancreatic beta cell development and that IGF-1 signaling in beta cells is largely through IRS2. The data further implicate IGF-1 signaling through IRS2 as a primary pathway that is required for an optimal complement of beta cells to develop. This application will extend these findings to determine underlying mechanisms for these hypothetical relationships. First, examination of tissue sections of embryo and adult mouse pancreas will be conducted to test the hypothesis that IRS2 is critical for proliferation and survival of islet precursor cells and identify the major site of developmental failure in mice lacking IRS2 protein. Second, the role of PI 3-kinase in mediating some of the effects of IRS2 in beta cell development will be examined. Third, experiments will be conducted to determine whether it is in fact the IRS2 lacking specifically in beta cells that causes diabetes in IRS2 gene knockout mice. IRS2 will be reintroduced into these animals, specifically in beta cells, and its effect on the diabetes syndrome monitored. Finally, disruption of IRS2 protein expression specifically in beta cells will be conducted to determine whether this is sufficient to cause diabetes, and specific hepatic disruption of IRS2 will be achieved as a presumed negative control.